Photolithography is commonly used during formation of integrated circuits on substrates. More specifically, a form of actinic energy (such as, for example, ultraviolet light) is passed through a radiation-patterning tool and onto an imaging material (e.g., photoresist) of a substrate. The radiation-patterning tool can be, for example, a photomask or a reticle, with the term “photomask” traditionally referring to masks which define a pattern for an entirety of a wafer substrate, and the term “reticle” traditionally being understood to refer to a patterning tool which defines a pattern for only a portion of the wafer substrate. However, the terms “photomask” (or more generally “mask”) and “reticle” are frequently used interchangeably so that either term can refer to a radiation-patterning tool that encompasses either a portion or an entirety of a wafer, and is so used herein. The actinic energy impinging upon the imaging material impacts the solubility of the exposed regions versus the unexposed regions in certain developing solvents. The imaging material is then solvent processed to remove one or the other of the exposed or the unexposed regions, thereby forming the imaging material to have mask openings extending partially or wholly there-through. The remaining patterned imaging material can then be used as a mask for processing underlying substrate material, such as, for example, ion implanting or etching through the openings in the imaging material.
In some instances, the primary features (i.e., features intended to be patterned into an imaging layer on the substrate) may be formed into an array of a repeating pattern. For example, primary features in the form of contact openings, trenches/indentations, and/or conductive lines may be formed within a device region or array to have uniform size, shape, and pitch. At the edges of the device region, optical proximity effects may occur which can make the primary features along the edges of the device region pattern differently than those that are away from the edges. One manner of contending with this adverse phenomenon is to use what are referred to as sub-resolution assist features at the edges of the device region. These assist features are made of a sufficiently small size and suitable material so that they are “sub-resolution” to the imaging material, meaning that they do not print on the substrate. A problem is now developing wherein the desired small sub-resolution assist features at the edges of the device region are getting too small to be created in fabrication of the photomasks.